Fuse cartridge



United States Patent 01 fee Int. Cl. H01h 85/40 US. Cl. 337-203 3 ClaimsABSTRACT OF THE DISCLOSURE The insulating body of the fuse has an axialconduit for passage of a cooling fluid such as air or de-mineralizedwater, the fusible elements being disposed in passages parallel to theaforesaid conduit and disposed around the latter. The end heads of thecartridge are annular in the case of air cooling and they form endcovers in the case of a cooling liquid.

This invention relates to fuse cartridges which are used for theprotection of electric lines against overloads or short circuits.

In such fuse cartridges the current which fiows through the fusibleelements under normal operating conditions generates heat and thuscauses an increase of the inner temperature of the cartridge. In fusecartridges of relatively small dimensions this heat is easilytransferred by conduction to the metallic end contacts where it isdissipated into the ambient atmosphere, but with big cartridges thiscooling effect is no more sufiicient and the temperature of thecartridge rises in a substantial manner when it is operated at its fullnominal rating. This is of course an important disadvantage since a hotcartridge will blow more easily (i.e. under a smaller current) than acool one. In actual practice the nominal rating of a cartridge islimited by the fact that under prolonged operation the fusible elementsmay reach their melting point under a load which they would easilywithstand in the cold state.

It has been proposed to enhance the cooling of fuse cartridges byproviding fins on the metallic end members of the cartridge. But ofcourse the cooling effect of such fins is limited by the rate of theheat trasfer between the fusible elements and the end membersthemselves. It has also been suggested to provide fins on the insulatingbody of the cartridge, but in big cartridges these fins are almostineffective owing to the heat-insulating character of the mass ofarc-quenching material in which the fusible elements are embedded and ofthe insulating body itself.

It is therefore an important object of the present invention to providea fuse cartridge in which the heat generated in the fusible elementswill be easily dissipated.

In accordance with the present invention a fuse cartridge comprises aninsulating body having a number of passages, each containing a fusibleelement embedded in a mass of arc-quenching substance, and a conduitthrough which a cooling fluid is circulated during operation of thecartridge.

Each fusible element together with the corresponding mass ofarc-quenching substance, may be considered as an elementary fusecartridge of reduced dimensions in which heat is relatively easilytransferred from the fusible element to the wall of the insulating bodyowing to the reduced thickness of the said mass. Since the insulatingbody itself is effectively cooled by the cooling fluid, this heat iseasily dissipated and therefore the general temperature of the cartridgeremains relatively low.

In a preferred embodiment the conduit for the cooling fluid issubstantially co-axial with respect to the insulat- 3,453,579 PatentedJuly 1, 1969 ing body and the passages containing the fusible elementsare disposed in a circular row around the said conduit. The coolingfluid may be a gas, such as air, or a liquid, as for instancede-mineralized water.

In the accompanying drawings:

FIG. 1 is a longitudinal section of an air-cooled fuse cartridgeaccording to the invention.

FIG. 2 is the corresponding end view with parts in section.

FIG. 3 is a longitudinal section of another embodiment wherein a liquidforms the cooling fluid.

In the embodiment of FIGS. 1 and 2, the fuse cartridge comprises a body1, made of a fire-proof insulating material of square cross-section inthe example illustrated, the said body being formed with an axial squareconduit 1a and with a number of passages 1b (four in the exampleillustrated) regularly disposed around the said con duit. Each passage1b, of elongated cross-section, contains a fusible ribbon 2 (as forinstance of silver) surrounded by a mass 3 of an appropriatearc-quenching material such as pulverulent silica, sand, etc. The endsof ribbons 2 are soldered to annular heads 4 secured to the ends ofinsulating body 1 by screws 5, these heads 4 having lateral extensions4a adapted to receive the electric conductors. A seal 6 is preferablyinserted between body 1 and each one of the annular heads 4 in order toprotect passages 1b. As illustrated the central hole of each head 4corresponds substantially to the cross-section of the axial conduit 1a.

Each passage 1b containing a single fusible ribbon 2, the mass 3 ofarc-quenching material required is of reduced importance and thereforeheat may be easily transferred from the fusible ribbon, where it isgenerated, to the insulating body 1 through the said mass. Owing to thereduced thickness of the insulating body between each passage 1b and theaxial conduit 1a, fliis heat is in turn easily transferred to the airwhich fills the conduit. The heated air flows upwardly from conduit 1aand is replaced by cold air from the surrounding atmosphere. Thiscirculation of cooling air may be greatly improved by disposing thecartridge vertically, the axial conduit thus forming a kind of chimneythrough which air flows regularly from the lower end to the upper end.

When the cartridge of FIGS. 1 and 2 is mounted on a rotating support, asthis sometimes occurs in electric machines such as alternators, theaxial conduit 1a is preferably disposed radially in order to operate asthe radial air passages of a centrifugal blower.

As illustrated in FIG. 2 the elongated passages 1b have a more or lesselliptical cross-section with the major axis thereof substantiallyparallel to the adjacent side of the square cross-section of the centralconduit. This arrangement reduces the thickness of the insulating wallbetween each passage lb and the axial conduit 1a, as also between eachpassage 1b and the outer surface of the insulating body 1.

Each fusible ribbon 2 is preferably pleated as indicated in FIG. 1, thefold lines or ridges 2a contacting alternately one and the other side ofthe corresponding passage 1b. This also increases the heat transfer ratebetween the strip and the insulating body. Owing to the ellipticalprofile of passages 1b, ample space is left for the fiow of pulverulentarc-quenching material during the filling operation of the cartridge.

It would obviously be possible to provide more than four pasages 1b, theaxial conduit being shaped accordingly. For instance the cartridge couldcomprise six passages suchas 1b disposed around a hexagonal axialconduit. The axial conduit could be of circular cross-section, moreparticularly in the case of a relatively high number of passages 1h, asfor instance six or more.

In the embodiment of FIG. 3 the end heads, here referenced 7, are in theform of covers which close the ends of the axial conduit 1a. Each headhas a nozzle 7b adapted to be connected with an appropriate coolingfluid line by means of which a suitable cooling fluid, such asdemineralized water, may be circulated through the cartridges. Annularseals 8, as for instance conventional 0- rings, are disposed incorresponding recesses of the inner side of heads 7 to prevent access ofthe cooling fluid to passages 1!). Owing to the high cooling power ofliquids, and more particularly of water, the cartridge of FIG. 3 may beoperated under a high load during long periods without any risk of aprogressive overheating of the fusible elements.

I claim: t

1. A cartridge fuse comprising a tubular insulating body having a firstend and a second end and having: an axial conduit extending between saidfirst and second ends, said tubular body being formed with a pluralityof openended substantially elliptical passages disposed therein aroundsaid conduit and extending between said first and second ends insubstantially parallel relation thereto; each of said passages having anelongated cross-section with a major axis and a minor axis, the minoraxis being disposed substantially radially with respect to said conduit;a pair of metallic contact heads adapted to receive electric conductorssecured respectively to said first and second ends, each of said headshaving an opening for passage of a cooling fluid through said conduit; aplurality of ribbon-like fusible elements each disposed in one of saidpassages and electrically connecting said metallic contact heads witheach other; said fusible elements being folded in ziz-zag formation withthe edges of the folds of the ribbon elements disposed parallel with themajor axes of the elliptical passages so that the corners of the foldscontact the tubular body within said passages; and a mass of arcquenching material filling each of said passages around each of saidfusible elements.

2. In a cartridge fuse as set forth in claim 1, the opening of each ofsaid heads registering substantially fully with said conduit of saidbody to permit free air circulation therethrough.

3. In a cartridge fuse as set forth in claim 1, the opening of each ofsaid heads being formed to permit circulation of a cooling liquidthrough said conduit.

References Cited UNITED STATES PATENTS 961,139 6/1910 Keller 13-182,713,098 7/1955 Swain 200'120 3,251,968 5/1966 Cameron 20O120 BERNARDA. GELHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.

U.S. Cl. X.R. 337-161, 186, 227

